In many agricultural applications it is important to control the depth of a ground engaging implement. In other agricultural applications, it is important to maintain an agricultural machine component above the soil a predetermined, fixed height. One example of the latter application is in a combine header used in the harvesting of crops. The individual heads must be maintained for a given height above the soil to avoid damage to the head caused by impact with the soil or other obstruction such as a rock. Positioning the header too close to the soil may also result in ingestion of non-crop debris which reduces harvesting efficiency and may also cause damage to the combine. The head must also not be raised too high to avoid missing down plants which do not extend upwardly a sufficient distance. The trend today is toward the use of larger headers having increased numbers of individual heads mailing it more difficult to monitor and adjust head height to avoid damage. A prime objective in crop harvesting is to cover as much ground as possible by operating at high speeds which increases the possibility of header damage caused by irregular terrain or hazards in the field. With increased combine operating speeds, monitoring and adjusting head height is made even more difficult. Header repairs are costly and time consuming.
There are various approaches to maintaining the header a predetermined height above the soil. One such approach employs a curved bar attached to an intermediate, lower portion of the head which engages the soil as the combine traverses a field. A chain couples a distal end of the bar to the head for preventing breakage of the bar in the event the bar engages a hazard in the field when the combine is put in reverse. The curved bar functions as a sensor, detecting the height of the head above the soil, and provides a feedback signal to a height controller in the combine for adjusting header height. This sensor mechanism is adapted for attachment to a head having a metal housing and is not easily mounted to current polyurethane head housings which are gaining increasing acceptance because of their light weight. In addition, the curved bar is attached to an intermediate portion of the head housing and thus sometimes provides a height adjustment signal too late to protect the forward end of the housing as it traverses a field. Another approach to header height control employs a pulsed ultrasonic system for determining and adjusting header height as the combine moves through a field. This latter approach is expensive and of limited reliability.
The present invention addresses the aforementioned limitations of the prior art by providing the combine header height detector and control which is particularly adapted for mounting to the leading end of a polyurethane head housing, is highly reliable and resistant to breakage, and is easily retrofit on existing headers.